We are developing a method for evaluating vestibular control of posture. Vision is eliminated by eye closure and kinesthetic cues are eliminated by rotating the supporting surface to null changes in ankle angle. Body sway is monitored by a video/computer system and torques generated by postural adjustments are monitored by semiconductor strain gages mounted on steel flexures that support a platform upon which the patient stands. We propose to develop and validate a vestibular function test, based on this method, that will make discriminations between vestibular and nonvestibular lesions, between semicircular canal and otolithic lesions, and between right-sided and left-sided lesions.